@eflexsystems/factory-bot/src/generators/Sequence.js

A factory library for Node.js and JavaScript inspired by factory_girl

import Generator from './Generator.js'

function generateId() {
  let id
  let i = 0
  do {
    id = `_${i++}`
  } while (id in Sequence.sequences) // eslint-disable-line no-use-before-define
  return id
}

class Sequence extends Generator {
  generate(id = null, callback = null) {
    if (typeof id === 'function') {
      callback = id
      id = null
    }
    id = id || this.id || (this.id = generateId())
    Sequence.sequences[id] = Sequence.sequences[id] || 1
    const next = Sequence.sequences[id]++
    return callback ? callback(next) : next
  }
}

Sequence.sequences = {}

Sequence.reset = (id = null) => {
  if (!id) {
    Sequence.sequences = {}
  } else {
    Sequence.sequences[id] = undefined
  }
}

export default Sequence